The proposed research is directed toward the long term goal of defining developmental factors which are crucial in differentiation and specification of neurons. Techniques previously applied to describe neurotransmitter phenotypic expression and development in the peripheral nervous system will be applied to the brain. Specifically, the embryonic and postnatal development of the adrenergic C1-C3 cell groups of the rat medulla oblongata will be studied to: 1) document the initial appearance of a range of adrenergic phenotypic characters, 2) define the temporal relationship between "neuronal birthdays" and the initial expression of adrenergic phenotypic characters, 3) compare central and peripheral adrenergic neurons witb respect to phenotypic expression, development and regulation by glucocorticoids, 4) elucidate possible transplacental effects of maternal glucocorticoids on adrenergic development in fetal brain, 5) investigate peptidergic expression in central adrenergic neurons, and 6) study the effects of target structures on adrenergic development. An interdisciplinary approach involving immunocytochemistry, biochemistry, autoradiography, pharmacology and cell culture will be taken. These studies promise to elucidate loci where changes in the milieu of the developing neuron may lead to abnormal neuronal development and ultimately to therapeutic approaches for the correction of neuronal deficits.